This invention relates to an apparatus for recording and reproducing information using a disk-shaped recording medium.
Recently, the importance of information recording/reproducing apparatus for recording and reproducing various information using a disk-shaped recording medium, such as a magnetic disk or an optical-disk, is increasing. This is attributable to the fact that the disk-shaped recording medium permits high density recording of data and access to recorded data at a comparatively high speed.
With the prior art information recording/reproducing apparatus using a magnetic disk or an optical-disk, the recording or reproduction of information is made on the basis of constant angular velocity (CAV) technique. The disk for storing desired information is rotated at a constant angular velocity for writing and reading information.
Commonly, a plurality of concentric circular tracks are formed on the surface of the recording disk, and each circular track is divided into a plurality of sections (which are called "sectors"). The information is written, i.e., stored, in the disk in successive sectors of tracks. It is also read out, i.e., reproduced, from successive sectors of tracks.
In the prior art information recording/reproducing apparatus, which adopts the CAV system, the angular velocity of the recording disk is fixed irrespective of the head's tracking position in the radial direction of the disk, i.e., irrespective of whether the head is tracing a track near the edge of the disk or a track near the center thereof. This means that the sectors in the individual circular tracks are aligned in the radial direction of the disk. More particularly, the start and end points of the sectors in the individual tracks are substantially aligned along lines radially extending from the center of rotation of the disk. Thus, in playback, the start point of a desired sector among a number of sectors can be relatively easily detected or retrieved since the start points of sectors are aligned along radial lines as described above.
In the prior art information recording/reproducing apparatus based on the CAV system, however, the quality of information stored in an outer track region near the edge portion of the disk is inferior compared to the quality of information stored in an inner track region near the center of the disk. That is, uniform high quality recording and reproduction of information cannot be obtained. In addition, longer arcuated sectors are required in the outer track region, and shorter arcuated sectors in the inner track region, for storing information consisting of the same number of bits. This means that the information recording density is lower the closer the track is to the edge of the disk. That is, uniform high density recording of information on the disk cannot be essentially obtained.
To overcome the drawbacks discussed above which are inherent in the prior art apparatus based on the CAV system, there has been developed an information recording/reproducing apparatus in which the recording disk is rotated on the basis of a constant linear velocity (CLV) technique. In such apparatus, the rotational disk speed, i.e., the angular velocity of disk, is continuously varied to provide a constant relative speed of the head and disk. In this case, the length of each sector is fixed irrespective of its position in the radial direction of the disk. Thus, it is possible to obtain recording and reproduction of information with uniformly high quality and uniformly high density over the entire disk surface. To date, various information recording/reproducing apparatuses adopting such system have been developed for the recording and reproduction of continuous data information such as video or audio signal.
However, where information is stored in successive sectors on the recording disk in the CLV system apparatus, the start and end points of sectors on the individual tracks are not aligned in radial directions of the disk. Therefore, an undesirably long time is required for retrieving a desired sector in playback.
Neither the prior art information recording/reproducing apparatus based on the CAV system nor the prior art information recording/reproducing apparatus based on the CLV system is capable of simultaneously storing data in successive sectors on the disk with uniformly high quality and density and retrieving a sector in which desired data is stored.